The invention relates to novel organosilicon compounds of the formula I
R1xe2x80x94(A1)mxe2x80x94Z1xe2x80x94A2xe2x80x94(Z2xe2x80x94A3)nxe2x80x94Wxe2x80x94SiXaYbZcxe2x80x83xe2x80x83I
in which
R1 is a chiral or achiral alkyl group having up to 10 carbon atoms, in which, in addition, one or two non-adjacent CH2 groups may be replaced by xe2x80x94Oxe2x80x94 atoms, or is F, Cl or a halogenated alkyl, alkoxy, alkenyl or alkenyloxy radical having 1 to 3 carbon atoms
A1, A2, and A3 are each, independently of one another,
a) a 1,4-cyclohexylene radical, in which, in addition, one or two non-adjacent CH2 groups may be replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94Sxe2x80x94,
b) a 1,4-cyclohexenylene radical, or
c) a 1,4-phenylene radical, in which, in addition, one or more CH groups may be replaced by N atoms,
where the radicals a), b) and c) may be substituted by one or two fluorine atoms,
Z1 and Z2 are each xe2x80x94CH2CH2xe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94C2H4xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94CH2CHCHxe2x95x90CH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94CH2xe2x80x94, xe2x80x94Oxe2x80x94CF2xe2x80x94, xe2x80x94CF2xe2x80x94Oxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94 or a single bond,
m is 0 or 1,
n is 0, 1 or 2 where m+n is xe2x89xa71,
W is a straight-chain or branched alkylene group having up to 10 carbon atoms, in which, in addition, one or two non-adjacent CH2 groups may be replaced by xe2x80x94CHFxe2x80x94 and/or xe2x80x94CH(CF3)xe2x80x94,
X, Y and Z are each, independently of one another, OCN, CN, Rxe2x80x2, ORxe2x80x2, H or Cl, where at least one of the substituents X, Y and Z is not H,
Rxe2x80x2 is an alkyl group having 1 to 15 carbon atoms, in which, in addition, one or more non-adjacent CH2 groups may be replaced by xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94 and/or xe2x80x94CHxe2x95x90CHxe2x80x94, and
a, b and c are 0, 1, 2 or 3, where a+b+c=3.
The compounds of the formula I are excellently suitable for the homeotropic alignment of liquid-crystalline phases on surfaces, for example glass plates, which may also be coated, as used in the production of electro-optical display elements. The alignment of liquid-crystalline phases oriented in this way can be modified by an external electric field owing to their negative dielectric anisotropy. They are suitable for use in displays operated on the principle of deformation of aligned phases (Appl. Phys. Lett. 19, 391 (1971)), the principle of dynamic scattering (Proc. IEE 56, 1162 (1968)) or the guest-host principle (Mol. Cryst. Liq. Cryst. 63, 19 (1981)).
It was hitherto technically quite difficult to produce a uniform and stable homeotropic alignment of liquid-crystalline phases. For example, the liquid-crystalline phase used has been doped with surface-active substances, such as lecithins, long-chain aliphatic amines, quaternary ammonium or phosphonium salts or carboxylatochromium complexes (Appl. Phys. Lett., 268 (1975)). Also common was coating of glass surfaces with said substances before introduction of the liquid-crystalline phase. However, the uniformity and stability of the resultant homeotropic alignment of liquid-crystalline phases are unsatisfactory.
German Patent Applications P 33 31 515 and P 36 01 742 disclose trialkanoyloxysilanes for producing a homeotropic alignment of liquid-crystalline phases on surfaces. However, these compounds have a number of disadvantages. For example, their preparation from acid anhydrides and trichlorosilanes is frequently accompanied by the formation of dark-brown byproducts, which can be separated from the desired trialkanoyloxysilane only with difficulty. Products contaminated in this way are not suitable for surface treatment, since they reduce the optical transparency of the substrate material. Furthermore, hydrolysis of the trialkanoyloxy compounds on the substrate surface by the process indicated in P 33 31 515, frequently results only in low-molecular-weight hydrolysis products, which are volatile with the steam used and thus do not contribute to the modification of the treated surface, which results in complete or only partial surface alignment of liquid-crystalline phases applied. Furthermore, it has been found in practice that the known alignment materials very frequently do not exhibit uniform perpendicular alignment, which means that complex processes, such as inclined vapour deposition, are stillxe2x80x94as also in most known organosilicon compoundsxe2x80x94necessary in addition to the alignment material.
There is, therefore, a demand for stable, novel organosilicon compounds which can be used to achieve uniform tilt without additional process steps having to be carried out.
The invention therefore had the object of enabling better, in particular more uniform and more stable homeotropic alignment of liquid-crystalline phases on surfaces. This object has been achieved by the provision of the compounds of the formula I.
The invention thus relates to the compounds of the formula I and to a process for their preparation, characterized in that an unsaturated compound of the formula II
R1xe2x80x94(A1)mxe2x80x94Z1xe2x80x94A2xe2x80x94(Z2xe2x80x94A3)nxe2x80x94Wxe2x80x94CHxe2x95x90CH2xe2x80x83xe2x80x83II
is reacted with a silane Hxe2x80x94SiXaYbZc, in which R1, A1, A2, A3, Z1, Z2, m, n, X, Y, Z, W, a, b and c are as defined above, or in that a halide of the formula III
R1xe2x80x94(A1)mxe2x80x94Z1xe2x80x94A2xe2x80x94(Z2xe2x80x94A3)nxe2x80x94Wxe2x80x94Halxe2x80x83xe2x80x83(III)
is reacted with a silane Hxe2x80x94SiXaYbZc, in which R1, A1, A2, A3, Z1, Z2, m, n, X, Y, Z. W, a, b and c are as defined above, and Hal is Cl, Br or I.
The invention furthermore relates to the use of the compounds of the formula I as components of liquid-crystalline dielectrics for electro-optical display elements, and to their use for producing homeotropic alignment of liquid-crystalline phases on surfaces. The compounds of the formula I also enable the surface tension to be matched to the liquid-crystalline mixture in the display. Furthermore, the compounds according to the invention have an antistatic action and are therefore highly suitable as adhesion promoters to the polymer films in the display. The silicon compounds may additionally be used to build up an ion-barrier layer.
The invention also relates to the use of compounds of the formula I in printing processes for producing homeotropic alignment of liquid-crystalline phases on surfaces.
The invention furthermore relates to liquid-crystalline dielectrics containing at least one compound of the formula I, and to electro-optical display elements containing dielectrics of this type and/or containing surfaces which have been treated with a compound of the formula I.
Above and below, R1, A1, A2, A3, Z1, Z2, n, X, Y, Z, W, Rxe2x80x2, a, b and c are as defined above, unless expressly stated otherwise.
According to the definitions of the various groups, the compounds of the formula I embrace those of the subformulae Ia to If:
Compounds of the formulae Ia, Ic and Ie are particularly preferred.
Above and below, PheF is 1,4-phenylene which is substituted by fluorine in the ortho-position to R1, and PheFF is 1,4-phenylene which is disubstituted by 15 fluorine in each ortho-position to R1. Cy denotes a 1,4-cyclohexylene group.
The compounds of the subformula Ia embrace the preferred compounds of the subformulae Iaa and Iai:
Particular preference is given to the compounds of the formulae Iaa, Iab, Iae, Iaf, Iag and Iai.
The compounds of the subformula Ib embrace the preferred compounds of the subformulae Iba to Ibh:
The compounds of the subformula Ic embrace the preferred compounds of the subformulae Ica to Icp:
Of these, the compounds of the subformulae Icc, Ica, Icp and Ich are particularly preferred.
The compounds of the subformula Id embrace the preferred compounds of the subformulae Ida to Idl:
The compounds of the subformula Ie embrace the preferred compounds of the subformulae Iea to Iel:
The compounds of the subformula If embrace the preferred compounds of the subformulae Ifa to Ifl:
In the compounds of the formulae above and below, X, Y and Z are preferably identical (a=b=c=1) and are preferably xe2x80x94ORxe2x80x2, in which Rxe2x80x2 is preferably an alkyl group having 1-8 carbon atoms, particularly preferably 1-5 carbon atoms, very particularly preferably 1-3 carbon atoms. Furthermore, one or more non-adjacent CH2 groups in Rxe2x80x2 may also be replaced by xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94 and/or xe2x80x94CHxe2x95x90CHxe2x80x94. X, Y and Z are furthermore also chlorine.
Accordingly, ORxe2x80x2 is preferably methoxy, ethoxy, propoxy, furthermore butoxy, pentoxy, hexyloxy, heptyloxy, octyloxy, nonyloxy, decyloxy or 2-oxapropyl (=methoxymethyl).
2-Oxabutyl (=ethoxymethyl) or 3-oxabutyl (=3-methoxyethyl), 2-, 3-, or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl, 1,3-dioxabutyl (=-methoxymethoxy), 1,3-, 1,4- or 2,4-dioxapentyl, 1,3-, 1,4-, 1,5-, 2,4-, 2,5- or 3,5-dioxahexyl, or 1,3-, 1,4-, 1,5-, 1,6-, 2,4-, 2,5-, 2,6-, 3,5-, 3,6- or 4,6-dioxaheptyl.
Very particularly preferred compounds are those of the formulae above and below in which X, Y and Z are methoxy, ethoxy, propoxy, isopropoxy or 1-methyl-3-oxabut-1-enyloxy.
X, Y and Z are furthermore also Rxe2x80x2, where Rxe2x80x2 has the preferred meanings already described elsewhere, and accordingly are preferably methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, 2-oxapropyl (=methoxymethyl), 2-oxabutyl (=ethoxymethyl) or 3-oxabutyl (=3-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl, 1,3-dioxabutyl (=methoxymethoxy), 1,3-, 1,4- or 2,4-dioxapentyl, 1,3-, 1,4-, 1,5-, 2,4-, 2,5- or 3,5-dioxahexyl, or 1,3-, 1,4-, 1,5-, 1,6-, 2,4-, 2,5-, 2,6-, 3,5-, 3,6- or 4,6-dioxaheptyl.
In the compounds of the formulae above and below, R1 is preferably fluorine or a chiral alkyl group having 1 to 10 carbon atoms, furthermore a chiral alkoxy group or another chiral oxaalkyl group. R1 is furthermore also Cl, OCF3, OCHF2, OCHxe2x95x90CF2, OCFxe2x95x90CF2, OCFxe2x95x90CF2, OCH2CF3, OCH2CHF2, OC2F5 or OCHFCF3.
The chiral groups of R1 generally contain not more than one chain branch. Preferred branched radicals R1 are isopropyl, 2-butyl (=1-methylpropyl), isobutyl (=2-methylpropyl), 2-methylbutyl, isopentyl (=3-methylbutyl); R1 may furthermore be 2-methyl-pentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methyl-butoxy, 2-methylpentoxy, 3-methylpentoxy, 1-methyl-hexyloxy, 1-methylheptyloxy, 2-ethylhexyloxy, 2-oxa-3-methylbutyl or 3-oxa-4-methylpentyl.
If the groups A2 and/or A3 are 1,4-disubstituted cyclohexylene groups, the substituents can be in the cis- or trans-position. The compounds having a trans-configuration are preferred.
Z1 and Z2 are preferably, independently of one another, a single bond, furthermore preferably a xe2x80x94CH2CH2xe2x80x94 or xe2x80x94COxe2x80x94Oxe2x80x94 group. They are furthermore also a xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94 group.
The parameter n can be 0, 1 or 2 and is preferably 1.
In the compounds of the formulae above and below, W is preferably a straight-chain alkylene group having 1-10 carbon atoms, particularly preferably having 2-6 carbon atoms, and accordingly is, in particular, xe2x80x94C2H4xe2x80x94, xe2x80x94(CH2)3xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94(CH2)5xe2x80x94, or xe2x80x94(CH2)6xe2x80x94, furthermore also xe2x80x94C2H4xe2x80x94CH2xe2x80x94, xe2x80x94(CH2)7xe2x80x94, xe2x80x94(CH2)8xe2x80x94, xe2x80x94(CH2)9xe2x80x94 or (CH2)10xe2x80x94.
Furthermore, one or two non-adjacent CH2 groups in W can also be replaced by xe2x80x94CHFxe2x80x94 or xe2x80x94CH(CF3)xe2x80x94 having a centre of chirality. Preference is given to groups such as, for example, xe2x80x94(CH2)2xe2x80x94CHFxe2x80x94CH2xe2x80x94, xe2x80x94(CH2)2xe2x80x94CH(CF3)xe2x80x94CH2xe2x80x94 or xe2x80x94(CH2)xe2x80x94CHFxe2x80x94(CH2)3xe2x80x94.
Furthermore, the alkylene group in W may also be branched and have a centre of chirality. Branched groups of this type generally contain not more than one chain branch. Preferred branched groups are, for example, isopropylene, 2-butylene, isobutylene, 2-methylbutylene, isopentylene, 2-methylpentylene, 2-ethylhexylene or 2-propylpentylene.
The various lists of particularly preferred meanings for the individual parameters are to be taken as merely illustrative and in no way have a limiting character.
Compounds of the formula I containing optically active carbon atoms cover the racemates and the corresponding optically active enantiomers, and mixtures thereof.
Some particularly preferred organosilicon compounds of the formula I are mentioned below (L1 and L2 are H or F): 
R1 in subformulae I1-I17 is preferably fluorine or straight-chain alkyl having up to 6 carbon atoms. Rxe2x80x2 is preferably methyl or ethyl. In the compounds of the formulae I1 to I17, the 1,4-phenylene rings and the cyclohexane rings may also be substituted by one or more fluorine atoms. Particular preference is given to 3,5-difluoro-1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene and furthermore 2,3-difluoro-phenylene.
The compounds of the formula I can be prepared by methods known per se, as described in the literature (for example in the standard works such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Vol. XIII, 5, Georg-Thieme-Verlag, Stuttgart), to be precise under reaction conditions which are known and suitable for said reactions. Use can also be made here of variants which are known per se, but are not mentioned here in greater detail.
Compounds of the formual I can be prepared for example, as follows: 
The silanes of the formula Hxe2x80x94SiXaYbZc are known or can be prepared by known methods, as described, for example, in the above literature.
The addition reaction of the silanes HSiXaYbZc onto the unsaturated alkenes of the formula II is advantageously carried out in the presence of an inert solvent, for example a halogenated hydrocarbon, such as dichloromethane, and at temperatures between 0xc2x0 C. and about 100xc2x0 C., advantageously at the boiling point. Silane is advantageously employed in excess. The addition of a noble-metal catalyst, for example a solution of H2PtCl6, in isopropanol is advantageous. The reaction can also be accelerated by addition of peroxides, such as diacetyl peroxide, and/or by irradiation with light. Further suitable catalysts are, for example, also platinum complexes with dicyclopentadiene or rhodium and nickel complexes.
Chiral compounds can be prepared using, for example, a catalyst prepared in situ from a palladium complex, for example [PdCl(xcfx80-C3H5)]2, and a monodentate chiral binaphthylphosphine compound, as described in J. Am. Chem. Soc. 1991, 113, 9887.
For use in printing processes, where the use of polar solvents is advisable, the reaction of the halosilanes of the formula I can be carried out in an excess of the relevant alcohol. Resultant solutions of organosilicon compounds of the formula I can then, if desired after removal of the salt formed during the reaction from the added organic base, be used directly for the surface coating.
The compounds of the formula I can be used directly for coating the surfaces to be treated. Particularly suitable for coating are oxidic surfaces, for example those of metal oxides, semi-metal oxides or nonmetal oxides, but in particular glass surfaces.
The coating is advantageously carried out by wetting the precleaned surfaces with an approximately 0.1 to 1% solution of a compound of the formula I in a solvent, such as, for example, a halogenated hydrocarbon, such as dichloromethane or 1,1,1-trichloroethane, or lower alcohols, and evaporating the solvent in the air. Heating or steam aftertreatment of the surface modified in this way, as in-the compound claimed in DE-A 33 31 515, is generally unnecessary in the case of the compounds of the formula I. A uniform, high-molecular-weight film which is capable of homeotropically aligning liquid-crystalline phases is formed. For uniform alignment, additional shear between two glass plates at elevated temperature may be necessary. In order to simplify handling of compounds of the formula I, they can be dissolved in a suitable inert solvent, such as, for example, 1,1,1-trichloroethane, immediately after their preparation and after removal of volatile reaction components by distillation, and stored in a bottle sealed with a septum stopper. By means of a syringe, only the amount required in each case is removed from the storage bottle, so that the remainder of the solution remains protected against hydrolysis through atmospheric moisture.
The compounds of formula I thus represent an effective means of producing a homeotropic alignment of liquid-crystalline phases on surfaces.
Another application of the compounds of the formula I is use for the preparation of liquid-crystalline pigments, for example through three-dimensional crosslinking of silanols prepared from the compounds of the formula I. Application of the silanols in the liquid state to a smooth substrate produces a film, which is hardened, removed from the substrate and comminuted to give platelet-like particles. Before further processing or use in surface coatings, in is particular automotive paints, printing inks and plastics, excessively large and small pigments are removed by a particle-size-selective separation process. The usable pigments have a particle diameter in the order of from 5 to 200 xcexcm, preferably from 5 to 100 xcexcm, in particular from 5 to 60 xcexcm. When a medium provided with the pigments according to the invention is applied to a surface, the platelet-like pigments automatically line up parallel to the surface owing to flow processes in the base coat or in the printing ink. However, one or more compounds of the formula I can also be added as dopants to liquid-crystalline dielectrics, these dielectrics containing from about 0.01 to 1% by weight, preferably from about 0.05 to 0.5% by weight, of compounds of the formula I.
The dielectrics according to the invention consist of from 2 to 25, preferably from 3 to 15, components, including at least one compound of the formula I. The other constituents are preferably selected from nematic or nematogenic substances, in particular known substances from the classes of the azoxybenzenes, benzylideneanilines, biphenyls, ter-phenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl cyclohexanecarboxylates, phenylcyclohexanes, cyclohexylbiphenyls, cyclohexylcyclohexanes, cyclo-hexylnaphthalenes, 1,4-biscyclohexylbenzenes, 4,4xe2x80x2-bis-cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines,phenyl- or cyclohexyldioxanes, phenyl- or cyclo-hexyldithianes, 1,2-biscyclohexylethanes, 1,2-bis-phenylethanes, 1-cyclohexyl-2-phenylethanes, optionally halogenated stilbenes, benzyl phenyl ethers, tolans and substituted cinnamic acids.
The most important constituents of such liquid-crystalline dielectrics of the suitable compounds may be characterized by the formula V,
Rxe2x80x2xe2x80x94Lxe2x80x94Gxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x83V
in which L and E are each a carbocyclic or heterocyclic ring system from the group formed by 1,4-disubstituted benzene and cyclohexane rings, 4,4xe2x80x2-disubstituted biphenyl, phenylcyclohexane and cyclohexylcyclohexane systems, 2,5-disubstituted pyrimidine and 1,3-dioxane rings, 2,6-disubstituted naphthalene, di- and tetrahydronaphthalene, quinazoline and tetrahydroquinazoline,
or a Cxe2x80x94C, single bond, Y is halogen, preferably chlorine, or xe2x80x94CN, and Rxe2x80x2 and Rxe2x80x3 are alkyl, alkoxy, alkanoyloxy or alkoxycarbonyloxy having up to 18, preferably up to 8, carbon atoms, or one of these radicals is alternatively CN, NCS, NC, NO2, OCF3, CF3, F, Cl or Br. The benzene and cyclohexane rings may also be substituted by F, Cl, xe2x80x94CN or xe2x80x94CH3.
In most of these compounds, Rxe2x80x2 and Rxe2x80x3 are different from one another, one of these radicals usually being an alkyl or alkoxy group. However, other variants of the proposed substituents are common. Many such substances and also mixtures thereof are commercially available.
The dielectrics according to the invention are prepared in a manner conventional per se. In general, the components are dissolved in one another, advantageously at elevated temperature.
By means of suitable additives, the liquid-crystalline dielectrics according to the invention can be modified in such a way that they can be used in all types of liquid-crystal display elements disclosed hitherto.
Additives of this type are known to the person skilled in the art and are described in detail in the literature. For example, conductive salts, for example ethyldimethyldodecylammonium 4-hexyloxybenzoate, tetrabutylammonium tetraphenylborate or complex salts of crown ethers (cf., for example, I. Haller et al., Mol. Cryst. Liq., Volume 24, pages 249-258 (1973)) can be added to improve the conductivity, dichroic dyes can be added to prepare coloured guest/host systems or substances can be added to modify the dielectric anisotropy, the viscosity and/or the alignment of the nematic phases. Such substances are described, for example, in DE-A 22 09 127, 22 40 864, 23 21 632, 23 38 281, 24 50 088, 26 37 430, 28 53 728 and 29 02 177.
The examples below are intended to illustrate the invention without representing a limitation. m.p.=melting point, cl. p.=clearing point. Above and below, percentage data are per cent by weight; all temperatures are given in degrees Celsius.